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arXiv 1705.01550astro-ph.GAastro-ph.COastro-ph.HE
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Swift/BAT AGN光谱调查(BASS)- VI。Gamma_X-L/L_Edd关系

The Swift/BAT AGN Spectroscopic Survey (BASS) -- VI. The Gamma_X - L/L_Edd relation

Benny Trakhtenbrot, Claudio Ricci, Michael J. Koss, Kevin Schawinski, Richard Mushotzky, Yoshihiro Ueda, Sylvain Veilleux, Isabella Lamperti, Kyuseok Oh, Ezequi… 展开作者

Benny Trakhtenbrot, Claudio Ricci, Michael J. Koss, Kevin Schawinski, Richard Mushotzky, Yoshihiro Ueda, Sylvain Veilleux, Isabella Lamperti, Kyuseok Oh, Ezequiel Treister, Daniel Stern, Fiona Harrison, Mislav Balokovic, Neil Gehrels

摘要:

本文研究了在Swift/BAT活动星系核光谱巡天(BASS)中选取的228个大样本的硬X射线低红移活动星系核(AGN)的吸积率(以L/LEdd表示)与硬X射线谱能量分布形状(即光子指数Gamma X)之间的观测关系。这包括30个活动星系核,其中黑洞质量(因此L/L_Edd)直接通过脉泽,空间分辨气体或恒星动力学,或混响映射测量。通过BASS提供的数据的高质量和广泛的能量覆盖范围使我们能够检查Gamma_X和L/L_Edd的几种替代测定。对于作为整体的BASS样本,我们发现Gamma_X和L/L_Edd之间的相关性在统计上显著,尽管非常弱。我们找到的最佳拟合关系为Gamma_X=0.15 log(L/L_Edd)+常数,比以前的研究报告要浅得多。此外,我们发现,不同的M_BH测定方法的活动星系核的子集之间没有相应的相关性。特别是,我们没有找到强有力的证据时,只考虑那些活动星系核与直接或单历元M_BH估计的相关性。后一个发现与以前几个研究相反,这些研究集中在z>0.5的宽线活动星系核上。我们讨论了这种紧张局势,并得出结论,它可以部分占,如果采用一个简化的,幂律的X射线光谱模型,结合L/L_Edd估计的基础上的连续发射和单历元宽线光谱的光学制度。最后指出了在深河外X射线巡天中使用Gamma_X探测超大质量黑洞演化的局限性。

英文摘要:

We study the observed relation between accretion rate (in terms of L/L_Edd) and shape of the hard X-ray spectral energy distribution (namely the photon index Gamma_X) for a large sample of 228 hard X-ray selected, low-redshift active galactic nuclei (AGN), drawn from the Swift/BAT AGN Spectroscopic Survey (BASS). This includes 30 AGN for which black hole mass (and therefore L/L_Edd) is measured directly through masers, spatially resolved gas or stellar dynamics, or reverberation mapping. The high quality and broad energy coverage of the data provided through BASS allow us to examine several alternative determinations of both Gamma_X and L/L_Edd. For the BASS sample as a whole, we find a statistically significant, albeit very weak correlation between Gamma_X and L/L_Edd. The best-fitting relations we find, Gamma_X=0.15 log(L/L_Edd)+const., are considerably shallower than those reported in previous studies. Moreover, we find no corresponding correlations among the subsets of AGN with different M_BH determination methodology. In particular, we find no robust evidence for a correlation when considering only those AGN with direct or single-epoch M_BH estimates. This latter finding is in contrast to several previous studies which focused on z>0.5 broad-line AGN. We discuss this tension and conclude that it can be partially accounted for if one adopts a simplified, power-law X-ray spectral model, combined with L/L_Edd estimates that are based on the continuum emission and on single-epoch broad line spectroscopy in the optical regime. We finally highlight the limitations on using Gamma_X as a probe of supermassive black hole evolution in deep extragalactic X-ray surveys.

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